1. Field of the Invention
The present invention relates to a working vehicle equipped with a ground working implement or cultivate machinery and a toroidal type of continuously variable transmission, which is capable of controlling the variator ratio in the toroidal mechanism for infinite variable-speed driving.
2. Prior Art
A working vehicle equipped with a ground working implement such as a combination of a cultivate tractor and a rotary cultivator is apt to suddenly produce a strong driving force in the forward direction at the outset when the rotary cultivator hits against a relatively hard soil in the cropland. The resultant sudden drive is the cause for unstable operation, accompanying uncontrollable acceleration. In the hope of solving this problem a driving speed control for the working vehicle is proposed in Patent Document 1.
The proposed driving speed control is so designed that the trunnion of the continuously variable transmission is responsive to any dashing(walking out) move when detected for making an associated hydraulic motor controllably rotate the trunnion, thereby suppressing the undesired speed variation.
Patent Document 2 proposes a working vehicle such as a cultivate tractor equipped with a PTO shaft for producing a working power and with a variable drive transmission for variably controlling the driving force, which variable drive transmission comprises a full-toroidal type of transmission contained in the transmission case. Specifically, the variable driving force is transferred from the outputting discs of the toroidal transmission to the intermediate transmission shaft via the planet gear mechanism. The intermediate transmission shaft is arranged parallel to the output discs. This arrangement effectively attains a relatively wide speed control and a forward and reverse drive with the null rotary cultivator power produced at its geared neutral position. At the same time, the simplification and downsizing in structure is advantageously attained by eliminating the main clutch from the transmission. Also advantageously, in the proposed variable drive transmission the toroidal transmission mechanism is so controlled that at the time of making the implement stop the geared neutral position may be reached to make the rotary cultivator power stop with the result that the vehicle body remains in the state of being stabilized at the time of starting next time. In case there is any deviation from the geared neutral position in the toroidal transmission when the working is made to stop, the initializing control is performed to bring the toroidal transmission to the controlled position where the deviation from the geared neutral position is reduced, thus putting the vehicle body in the state of being stabilized at the subsequent startup.    Patent Document 1: Patent Application Laid-Open No. 2002-320402    Patent Document 2: Patent Application Laid-Open No. 2003-74659